Develop and Configure Private Shopify App for write_own_subscription_billing Permission

I have created a private Shopify app in my Shopify Partners portal and obtained all the necessary credentials except for the subscription permissions. The app, which needs to be developed, should be hosted on my cPanel and built using Node.js. The app's functionality includes deducting a 2% fee automatically from every processed order and handling payments through the Shopify Partners Portal. I need assistance with fully developing the app, including configuring and obtaining the write_own_subscription_billing permission via the Shopify API. Let me know if you can set this up from scratch! Ideal skills include expertise in Shopify API, Node.js development, and private app configuration.